1. Field of the Invention
The invention relates to the field of ultrasound imaging, particularly for medical applications.
2. Prior Art
In recent years, more emphasis has been placed on the use of ultrasound for medical diagnostics. Unlike x-rays which are known to be harmful, the levels of ultrasound energy used for diagnostics have been shown to be safe. In general, ultrasound scanners can be divided into two categories, those using phased arrays and those using separate transducers. The present invention relates to the latter category.
Scanners employing a plurality of transducers are used to provide continuous real time untrasound images. Such scanners are shown in U.S. Pat. No. 4,231,373 and U.S. Pat. No. 4,269,066.
The present invention uses a configuration of two transducers referred to as "split" transducers. Each transducer has a generally semicircular face; when the transducers are mounted their faces present a general circular shape. One advantage to this configuration is that the beams from both transducers are substantially coincident.
In the prior art, there are teachings for using split transducers for a continuous ultrasound Doppler examination. In this configuration, one transducer transmits a continuous ultrasound signal while the other transducer receives the echo. Crystal controlled filtering is used to sense the Doppler shift which is, by way of example, proportional to the velocity of blood flow. This Doppler technique is discussed in Ultrasound and the Diagnosis of Cardiovascular-Pulmonary Disease by Joyner, beginning at page 9, published by Yearbook Medical Publishers, Inc., 1974.
Applicant is aware of a research project where a split transducer configuration was used to provide a simultaneous B-scan and pulsed Doppler display. This prior art apparatus was a very large experimental unit, not susceptible to being hand-held. This experimental unit did not provide the wide range of operating modes described in this application. The short fluid path between the transducers used in the present invention and the patient were not employed, making the unit impractical for many types of examinations, such as complete cardiac examinations.
As will be seen, the present invention provides a scanning apparatus employing a split transducer. The apparatus can be used in a plurality of modes and combination of modes, such as B-scan, M-scan, pulsed Doppler and continuous Doppler. The apparatus is small and easily hand-held, allowing it to be used for cardiac examinations in addition to other examinations.